Flexible spine stabilization system

ABSTRACT

A system for flexibly stabilizing a vertebral motion segment by connecting a first vertebra and a second vertebra is disclosed. The system includes an elongate connection element with end portions interconnected by a flexible coupling member. The system includes first and second attachment portions for connecting the connection element to the vertebrae. A first resilient member is positioned between the first end portion and the first attachment portion, and a second resilient member is positioned between the first attachment portion and the second attachment portion. The system is designed such that the second resilient member is compressed when the first and second attachment portions move towards each other, and the first resilient member is compressed when the first and second attachment portions extend away from each other.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims is a continuation application of U.S. patentapplication Ser. No. 12/122,096 filed on Apr. 30, 2008 which claimspriority to U.S. Provisional Application Ser. No. 60/914,993 filed onApr. 30, 2007, which is incorporated herein by reference in itsentirety.

FIELD OF THE INVENTION

The present disclosure generally relates to flexible stabilizationsystems for spinal motion segment units. In particular, certainembodiments are directed to a soft stabilization system including atleast two bone fasteners and a flexible portion conformable to thenatural spinal movement.

BACKGROUND OF THE INVENTION

The spine includes a series of joints routinely called motion segmentunits, which is the smallest component of the spine that exhibitskinematic behavior characteristic of the entire spine. The motionsegment unit is capable of flexion, extension, lateral bending andtranslation. The components of each motion segment unit include twoadjacent vertebrae and their apophyseal joints, the intervertebral disc,and the connecting ligamentous tissue. Each component of the motionsegment unit contributes to the mechanical stability of the joint.

Components of a motion segment that move out of position or becomedamaged can lead to serious pain and may lead to further injury to othercomponents of the spine. Depending upon the severity of the structuralchanges that occur, treatment may include fusion, discectomy, orlaminectomy.

Underlying causes of structural changes in the motion segment unitleading to instability include trauma, degeneration, aging, disease,surgery, and the like. Thus, rigid stabilization of one or more motionsegment units may be an important element of a surgical procedure incertain cases (i.e., injuries, deformities, tumors, etc.), whereas it isa complementary element in others (i.e., fusion performed due todegeneration). The purpose of rigid stabilization is the immobilizationof a motion segment unit.

As mentioned above, current surgical techniques typically involve fusingone or more unstable motion segment units and possibly, the removal ofligaments, bone, disc, or combinations thereof included in the unstablemotion segment unit or units prior to fusing. There are severaldisadvantages to fusion, however. For example, the fusing processresults in a permanent or rigid internal fixation of all or part of theintervertebral joints and usually involves metallic rods, plates, andthe like for stabilization. In all cases, the systems are intended torigidly immobilize the motion segment unit to promote fusion within thatmotion segment unit.

In addition to a loss of mobility, fusion also causes the mobility ofthe motion segment to be transferred to other motion segments of thespine. The added stresses transferred to motion segments neighboring ornearby the fused segment can cause or accelerate degeneration of thosesegments. One other disadvantage to fusion is that it is an irreversibleprocedure. In addition, it is believed that fusion of a motion segmenthas a clinical success of approximately 70 percent, and often does notalleviate pain experienced by the patient.

Thus, while such fusion systems have been used since the early 1960's,the intentionally rigid designs have often caused stress concentrationsand have directly and indirectly contributed to the degeneration of thejoints above and below the fusion site (as well as at the fusion siteitself). In addition, rigid, linear bar-like elements eliminate thefunction of the motion segment unit. Finally, removal of portions of themotion segment unit reduces the amount of support available for theaffected motion segment unit.

Fusion procedures can be improved by modifying the load sharingcharacteristics of the treated spine. Thus, it would be desirable toallow more of a physiologic loading between pedicular fixation andanterior column support. It would also be desirable to have a devicethat precludes or at least delays the need for fusion for all but themost advanced degeneration of a motion segment, particularly if such adevice would allow close to normal motion and pain relief.

Thus, a need exists in the art for a soft spine stabilization systemthat replicates the physiologic response of a healthy motion segment.

SUMMARY

According to one aspect, a flexible spinal stabilization system that canprovide load sharing either as an enhancement to a fusion device or as amotion-preserving non-fusion device is provided.

According to another aspect, a flexible prosthesis for intervertebral orintersegmental stabilization designed to load share with a graft in theanterior column that allows for graft resorption while ensuringcompressive loading on the graft for fusion procedures in the spine isprovided.

Another embodiment is directed towards a device for intervertebral orintersegmental stabilization designed to ensure proper alignment andmotion between vertebrae of the spinal column that helps partiallyunload the discs and facet joints to give pain relief.

According to another aspect, a flexible connection element may be usedto as part of various components of a spine stabilization system. Forinstance, the flexible connection element may form all or part of onelongitudinal stabilization members. In another aspect, the flexibleconnection element may also form at least part of a transconnector.Depending on what component of the spine stabilization system uses theinvention, fasteners may also be connected to the component. Forinstance, in one embodiment the flexible connection element is connectedto bone fasteners, such as pedicle screws or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one embodiment of a flexible connectionelement according to the invention;

FIG. 2 is a perspective view of another embodiment of a flexibleconnection element;

FIG. 3 is a cross-sectional view of another embodiment of a flexibleconnection element;

FIG. 4 is a posterior view of one embodiment of a spine stabilizationsystem of the invention;

FIG. 5 is an exploded view of one embodiment of a stabilization systemaccording to the invention with an alternate embodiment of a flexibleconnection element;

FIGS. 5A-5C are side views of the embodiment of FIG. 5 in a neutralposition and extension positions;

FIG. 6 is an exploded view of one embodiment of an end portion of theflexible connection element of FIG. 5;

FIG. 7 is an assembled view of the end portion of FIG. 6 shown in afirst position;

FIG. 8 is an assembled view of the end portion of FIG. 6 shown in asecond position;

FIGS. 8A-8B are exploded perspective and exploded cross-sectional views,respectively, of an embodiment of another end portion of the flexibleconnection element of FIG. 5;

FIGS. 8C-8D are assembled perspective and assembled cross-sectionalviews, respectively, of the embodiment of FIGS. 8A-8B;

FIGS. 9-10 are exploded views of an embodiment of another end portion ofthe flexible connection element of FIG. 5;

FIG. 11 is a partial assembled view of the end portion of FIGS. 9-10shown in a second position;

FIG. 12 is a cross-sectional view of the end portion of FIGS. 9-11 shownin a second position;

FIGS. 12A-12B are exploded perspective and exploded cross-sectionalviews, respectively, of an embodiment of another end portion of theflexible connection element of FIG. 5;

FIGS. 12C-12D are assembled cross-sectional views of the embodiment ofFIGS. 12A-12B;

FIG. 13 is a perspective view of another embodiment of a flexibleconnection element;

FIG. 14 is a side view of another embodiment of a flexible connectionelement;

FIGS. 15-16 are perspective views of alternate embodiments ofstabilization systems according to the invention each with alternateembodiments of a flexible connection elements;

FIG. 17 is a perspective view of another embodiment of a stabilizationsystem;

FIG. 18 is an exploded view of another embodiment of a flexibleconnection element;

FIG. 19 is an exploded view of another embodiment of a flexibleconnection element;

FIGS. 20-22 depict an alternate end portion of a flexible connectionelement according to the invention;

FIG. 23 is a perspective view of another flexible connection element;

FIGS. 24-25 are perspective and cross-sectional views, respectively, ofanother embodiment of a flexible connection element;

FIG. 26 is an exploded view of another embodiment of a flexibleconnection element;

FIG. 27 is an exploded view of another embodiment of a flexibleconnection element;

FIG. 28 is an exploded view of another embodiment of a flexibleconnection element;

FIGS. 29-30 are perspective and exploded views, respectively, of anotherembodiment of a flexible connection element;

FIGS. 31-32 are perspective and exploded views, respectively, of anotherembodiment of a flexible connection element;

FIGS. 33-34 are perspective and exploded views, respectively, of anotherembodiment of a flexible connection element;

FIG. 35 is an cross-sectional view of another embodiment of a flexibleconnection element;

FIGS. 36-37 are perspective and exploded views, respectively, of anotherembodiment of a flexible connection element;

FIG. 38 is a perspective view of another embodiment of an end portionaccording to the invention;

FIGS. 39-40 are perspective and partial exploded views, respectively, ofanother embodiment of a flexible connection element;

FIG. 41 is a perspective view of another embodiment of a flexibleconnection element;

FIG. 42 is a perspective view of another embodiment of an end portionaccording to the invention;

FIGS. 43-45 are perspective, top, and cross-sectional views,respectively, of another embodiment of a flexible connection element;

FIG. 46 is a perspective view of another embodiment of a flexibleconnection element;

FIG. 47 is an exploded view of another embodiment of a flexibleconnection element;

FIG. 48 is a perspective view of another embodiment of a flexibleconnection element;

FIG. 49 is a perspective view of another embodiment of a flexibleconnection element;

FIGS. 50-52 are perspective views of additional embodiments of flexibleconnection elements; and

FIGS. 53-54 depict another embodiment of a flexible connection element.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Embodiments of the disclosure are generally directed to flexiblestabilization systems for use with the anterior, antero-lateral,lateral, and/or posterior portions of at least one motion segment unitof the spine. The systems of the invention are designed to beconformable to the spinal anatomy, so as to be generally less intrusiveto surrounding tissue and vasculature than existing rigid stabilizationsystems.

Certain embodiments may be used on the cervical, thoracic, lumbar,and/or sacral segments of the spine. For example, the size and massincrease of the vertebrae in the spine from the cervical to the lumbarportions is directly related to an increased capacity for supportinglarger loads. This increase in load bearing capacity, however, isparalleled by a decrease in flexibility and an increase insusceptibility to strain. When rigid immobilization systems are used inthe lumbar segment, the flexibility is decreased even further beyond thenatural motion restriction of that segment. Replacing the conventionalrigid immobilization systems with certain embodiments disclosed hereinmay generally restore a more natural movement and provide added supportto the strain-susceptible area.

One embodiment of a spine stabilization system described herein includesat least two bone fasteners and at least one flexible connection elementextending at least partially between the bone fasteners. In general, theflexible connection element may advantageously provide desirableproperties for bending or twisting that allows the system to accommodatenatural spine movement. According to some embodiments, the flexibleconnection element approximates or resembles a relatively circularcross-section tube or rod. In alternate embodiments, a flexibleconnection element may have other shapes as well. For instance theflexible connection element may have a cross-section that approximatesor resembles a circle, an oval, an ellipse, or angular geometric shapessuch as triangles, squares, rectangles, trapezoids, or the like. In manyembodiments, the flexible connection element may be made from more thanone component and the flexible connection element may have complex andvaried cross-sections along its length. It should be understood that inthese examples the different types of flexible connection elementsdescribed herein may be replaced or interchanged with a flexibleconnection element having different shapes or configurations, includingthe many variations described herein.

Embodiments of the present disclosure may also be used as a cross-braceor transconnector in communication with two rods along a portion of thelength of the spine. It is well known that the strength and stability ofa dual rod assembly can be increased by coupling the two rods with atransconnector that extends across the spine in a direction that isgenerally perpendicular to the longitudinal axes of the rods. When usedas a transconnector, the disclosed embodiments may include a firstfastener connecting the transconnector to a first rod and a secondfastener connecting the transconnector to a second rod. Alternatively,the transconnector may be connected to one or more bone fastenersassociated with a rod. Examples of transconnector designs that may beimproved by the present disclosure are described in U.S. Pat. No.5,743,911 to Cotrel, U.S. Pat. No. 5,651,789 to Cotrel, U.S. Pat. No.6,139,548 to Errico, U.S. Pat. No. 6,306,137 to Troxell, U.S. Pat. No.5,947,966 to Drewry, U.S. Pat. No. 5,624,442 to Mellinger, and U.S. Pat.No. 6,524,310 to Lombardo, all of which are incorporated herein in theirentirety.

As explained in greater detail below, the flexible connection elementcan be configured in many different ways. For instance, the flexibleconnection element may be a relatively straight connection element, suchas shown in FIG. 1. Alternatively, the flexible connection element mayhave a curved shape that corresponds approximately to the naturalcurvature of the portion of the spine that it supports. In eachembodiment, the flexible connection element may be made of one or morecomponents that are configured to allow the element to flex, bend, ortwist.

The Flexible Connection Element

Embodiments of the flexible connection element generally providestability, strength, flexibility, and resistance without the traditionalrigidity of prior systems. While the flexible connection element may bedesigned in a variety of ways according to the invention, the types ofdesign may differ depending on the final implementation of the system,i.e., lateral, posterior, etc. In a posterior application, for example,the flexible connection element may include a straight or curved profilealong its length.

Referring to FIG. 1, one embodiment of a flexible connection element 10is shown. Connection element 10 generally comprises first and second endmembers or portions 12, 14 and an intermediate portion or spacer 16disposed therebetween. End portions 12, 14 and spacer 16 are disposedabout a coupling member, such as a tether, cable, or cord 18 and extendalong a longitudinal axis 20. End portions 12, 14 are configured anddimensioned to be accepted and retained by a bone fastener or anchorsuch as a pedicle screw 34 or laminar hook. In general, end portions 12,14 are made from a generally rigid material such as, for example,titanium or any other known biocompatible metal or rigid material.Intermediate portion 16 may be a flexible or resiliently deformablemember that provides force absorbing effect in transmitting spinalcolumn loads between the anchors to which flexible connection element 10is engaged. Intermediate portion 16 may also permit relative movementbetween first and second end portions 12, 14.

Various embodiments of flexible connection element 10 contemplatevarious alternative configurations of end portions 12, 14 intermediateportions 16, and/or techniques for securing end portions 12, 14. As bestseen in FIG. 1A, end portions 12, 14 may be in the form of spools andmay have a generally barbell shaped body 22 with a middle body portion24 extending between end plates or flanges 26. The spacing betweenflanges 26 and the size of middle portion 24 may be dimensioned to fitwithin preexisting pedicle screw systems, such as those having anupright yoke or tulip-like receptacle. For instance, middle portion 24may have a cylindrical shape and may be received in a pedicle screwsimilar to a cylindrical rod in other known stabilization systems. Achannel or opening 27 may extend at least partially through body 22 foraccommodating a coupling element or cord 18. In alternate embodiments,such as those shown in FIGS. 2 and 3, spool members 12, 14 may have oneend plate or flange 26 configured to engage intermediate portion 16 andthe opposing end 28 may be cylindrical or rod shaped and may not have aflange. Cord 18 may extend entirely through the spools, as shown inFIGS. 1 and 2, or cord 18 may extend only partially within spools 12,14, as shown in FIG. 3.

According to the embodiment of FIG. 1, end portions or spools 12, 14 maybe affixed to cord 18 and intermediate portion 16 may be slidable ormoveable with respect to cord 18. Any known means or method may be usedto secure or affix cord 18 to spools 12, 14. According to one variation,a mechanical clamping member such as a set screw may be used to affixspools 12, 14 to cord 18. In the embodiment of FIG. 3, cord 18 may becrimped, glued, or otherwise secured to spools 12, 14. In alternateembodiments discussed in more detail below, one or more spools 12, 14may be slidable or moveable about cord 18.

Intermediate portion or spacer 16 may be made from a flexible, soft,and/or elastically resilient or deformable biocompatible material suchas for example, a biocompatible elastomer, silicone, polyurethane orpolycarbonate urethane or any other known similar material. Theintermediate portion may vary somewhat in shape, size, composition, andphysical properties, depending upon the particular joint or level forwhich the implant is intended. The shape of the body of the intermediateportion should complement that of the adjacent end portion(s) or platesto which it engages to allow for a range of translational, flexural,extensional, and rotational motion, and lateral bending appropriate tothe particular joint being replaced. The thickness and physicalproperties of the intermediate portion should provide for the desireddegree of elasticity or damping. However, the intermediate portionshould be sufficiently stiff to effectively cooperate with the endportions to limit motion beyond the allowable range.Polyurethane-containing elastomeric copolymers, such aspolycarbonate-polyurethane elastomeric copolymers andpolyether-polyurethane elastomeric copolymers, generally havingdurometer ranging from about shore 80 A to about shore 100 A and betweenabout shore 30 D to about shore 65 D have been found to be particularlysuitable for vertebral applications. If desired, these materials may becoated or impregnated with substances to increase their hardness orlubricity, or both.

In some embodiments, intermediate portion 16 has a generally cylindricalor tubular shaped body with a channel 30 extending longitudinallytherethrough. Channel 30 may be appropriately sized and dimensioned foraccommodating the coupling member or cord 18 therethrough. In theembodiment of FIG. 1, spacer 16 has a cylindrical profile and theexternal diameter 32 may be about the same as the diameter of flange 26of end portions 12, 14. Alternatively, spacer 16 may be smaller orlarger in diameter, or may be variable in diameter. According to oneembodiment, intermediate portion 16 may range in length depending on theapplication or surgeon preference. For instance, spacer 16 may bebetween about 4 mm and 38 mm, and in a kit a multitude of differinglengths and dimensions may be provided. One skilled in the art willappreciate that the flexibility of the connection element 10 may bechanged by the selection of the intermediate portion material and/orvarying its dimensions.

Coupling member or cord 18 may be made from polyethylene terephthalateor (PET), ultra high molecular weight (UHMW) polyethylene such asDyneema® or any other known material. The cord may also be formed usinga braided or stranded wire or synthetic or any combination as desired.The strands may be formed from identical materials or may differ fromeach other. For example, one strand may be wire, whereas other strandsmay be rubber-based. In the embodiment of FIG. 1, cord 18 may also bemade from, or additionally contain, an elastic material selected toallow the cord to elastically deform along its longitudinal axis. Inthis regard, depending on the selected material, cord 18 may elasticallystretch or elongate along axis 20. In other embodiments, cord 18 may bedesigned to have a constant length so as to not stretch or elongatealong its length. It will be clear to one skilled in the art that thestructure, length and diameter of the coupling member will affect theflexibility of the connection element 10.

Referring to FIG. 4, when end portions 12, 14 are retained by respectivebone fasteners 34, for example, and affixed to adjacent vertebrae, theconnection element 10 provides stability while simultaneously permittingmotion to the vertebrae in six degrees of freedom (i.e., x-axis, y-axis,z-axis, pitch, roll and yaw). Although the spacer 16 substantiallylimits the motion of the spools 12, 14 in the longitudinal axialdirection, the compressibility of the spacer 16 and elasticity of cord18 between the spools 12, 14 allows for stabilized motion of the spools12, 14 in each of the six degrees of freedom while also providing aresistance and stability of motion in each of the six degrees offreedom. The intermediate portion 16 maintains the end portions 12, 14in a substantially spaced relation, while allowing some relativemovement of the spacer 16 when external forces cause the spacer body tobend or compress in any direction.

In some embodiments, the flexible connection element may be configuredand adapted to exhibit preload forces even when the flexible portion isnot undergoing externally applied torsional, axial, or bending loads. Inthis regard, the coupling member or cord 18 may be pre-tensioned so thatthe end portions 12, 14 are compressed against the intermediate portion16 when engaged thereto. The amount of pre-tension can range from 0 tothe tensile break strength of the coupling member of cord. The greaterpre-tension loading of the cord generally results in a stifferconstruct. This preloaded configuration may be beneficial for designinga preferential response to different types of external forces orloading. For instance, a preloaded flexible connection element mayprovide a greater resistance to torsional loads that would tend tofurther tighten the flexible connection element due to added frictionalforces resisting sliding movement of the edges against each other.

Referring to FIG. 5, in another embodiment of a flexible connectionelement 40, a bumper or other resiliently compressible member 42 may bedisposed over cord 18 and positioned adjacent an outer end plate 44 ofan end portion or spool 45. A rigid stop, flange, or end member 46 maybe fixedly attached or clamped to cord 18 on the opposite side of bumper42 from the spool 45. In this embodiment, spool 45 may be slidable,movable, or otherwise unconstrained with respect to cord 18. In thisregard, bumper 42 may be resiliently compressed between spool 45 andstop 46 when spools 45, 47 are separated or forced apart in thelongitudinal direction of axis 20. For example, referring to FIGS.5A-5B, in one embodiment when spools 45, 47 are retained by respectivebone fasteners 34 and affixed to adjacent vertebrae, such aconfiguration facilitates the separating movement between spools 45, 47and the respective bone fasteners to which they are attached. Referringto FIG. 5A, showing connection element 40 in a first or neutral positionwith an overall length L1, spools 45, 47 may have a first separationdistance L2. As shown in FIG. 5B, in a second position, after aseparating movement between spools 45, 47, the second separationdistance L3 is greater than L2 which replicates a change in theseparation distance of the bone fasteners and the bone segments to whichthey are attached. Referring to FIG. 5C, one may appreciate that such afeature may be desired to replicate the natural kinematics that a spinalmotion segment undergoes under flexion wherein the elongation of theintrapedicular distance typically occurs. In one variation, the flexibleelement may accommodate up to 8 mm of a change in intrapediculardistance under flexion. In another variation, up to 4 mm of a change inintrapedicular distance may be accommodated. Such elongation may beaccomplished independent from or, in addition to, any elongation in cord18. In this regard, the degree or extent to which flexible connectionelement 40 may elongate may be designed, preselected, or predicted witha greater degree of accuracy than reliance on elasticity or elongationin the cord alone. In one embodiment, bumper 42 may be made from thesame material as intermediate portion 16. In alternate embodiments,bumper 42 may be made from a different material than intermediateportion 16 or bumper may be made from the same material and have adifferent hardness or flexibility than intermediate portion 16.

As shown in the embodiment of FIG. 5, an alternative end portion orspool 47 may be provided adjacent one end of flexible connection element40. As best seen in FIGS. 6-7, spool 47 generally comprises a middleportion 50 interposed between outer end plates or flange portions 52. Acentral channel 54 extends axially through spool 47 and is generallyconfigured and dimensioned to accommodate coupling member or cord 18.Middle portion 50 generally comprises a lower clamp body 56 and an upperclamp body 58 selectably moveable with respect to lower clamp body 56 toclamp down and affix cord 18 with respect to spool 47. In one variation,upper clamp body 58 has a pair of downwardly extending arms 60 havingelongated openings 62 configured and dimensioned to receive protrusionsor prongs 64, 66 extending outward from lower clamp body 56 so as toallow unidirectional one step clamping or locking of spool 47 withrespect to cord 18. Arms 60 are configured and dimensioned to deflect orbend outward slightly to move over protrusions 64, 66. In this regard,protrusions 64, 66 may have a chamfer or angled outer surface 68 andarms 60 may have a chamfered, beveled, or angled inner lower surface 70to facilitate arm deflection. Upper clamp body 58 may be firstpreassembled onto lower clamp body and positioned in a first position asshown in FIG. 7. In operation, as upper clamp body 58 is forceddownward, the arms 60 may engage upper prongs 64 and deflect outward andover the upper prongs 64 such that the upper prongs extend throughopenings 60 and provisionally maintain upper clamp body 58 in the firstposition. As shown in FIG. 7, in the first position, upper clamp body 58may be relatively loosely affixed to lower clamp body 56 such that acord extending through middle portion 50 may slide or move with respectto spool 47. To affix or clamp cord 18 with respect to spool 47 upperclamp body 58 may be forced downward further onto lower clamp body 56and positioned in a second or locked position as shown in FIG. 8. Inoperation, as upper clamp body 58 is forced downward, the arms 60 mayengage lower prongs 66 and deflect outward and over the lower prongs 66such that the lower prongs extend through openings 60 and maintain theupper clamp body 58 in the second, clamped, or locked position. As shownin FIG. 8, in the second position, upper clamp body 58 may be relativelyrigidly affixed to lower clamp body 56 such that a cord extendingthrough middle portion 50 may not slide or move with respect to spool47. One skilled in the art may appreciate that such a one step lock orclamping feature may be desirable to allow for tensioning of cord 18during installation in situ. Referring again to FIG. 5, one my alsoappreciate that with such a clamping feature integrated into the middleportion 50 of spool 47, the step of clamping or locking the cord may beaccomplished by finally tightening down on a cap 35 or set screw 36 of apedicle screw assembly 34. In this regard, the tensioning and finalclamping of cord 18 may be accomplished with a familiar procedure commonto the installation of contemporary spinal stabilization systems.

Referring to FIGS. 8A-8D, another embodiment of a spool 47 is disclosedwhich generally comprises a post or piercing means to affix cord 18 withrespect to spool 47. In one variation, upper clamp body 58 has a centralfinger or post 72 extending downwardly from the underside thereof. Inone variation, the post 72 may be configured and dimensioned to extendthrough the cord 18 so as to puncture or pierce through cord 18 and thedistal tip 73 of post 72 may enter into a depression 74 provided on theinterior of lower clamp body 56. As with the above described embodiment,a pair of arms 76 extend downward from upper clamp 58 are configured anddimensioned to engage lower clamp body 56 so as to allow unidirectionalone step clamping, piercing, and/or locking of spool 47 with respect tocord 18. As shown in FIGS. 8A-8B, in a first position, upper clamp body58 may be spaced from or relatively loosely affixed to lower clamp body56 such that a cord extending through middle portion 50 may slide ormove with respect to spool 47. To affix or clamp cord 18 with respect tospool 47 upper clamp body 58 may be forced downward further onto lowerclamp body 56 and positioned in a second or locked position as shown inFIGS. 8C-8D. As shown in FIGS. 8C-8D, in the second position, upperclamp body 58 may be relatively rigidly affixed to lower clamp body 56such that a cord extending through middle portion 50 may not slide ormove with respect to spool 47.

Referring to FIGS. 9-12, one embodiment of a clamp assembly 80 forclamping rigid stop, flange, or end portion 46 to cord 18 is shown.Clamp assembly 80 generally comprises an annular end body 82 having anend plate or flange 84 and a central cavity 86 configured anddimensioned to house a lower clamp body 88 and an upper clamp body 90.Upper and lower clamp bodies 90, 88 have a tapered or partiallyconically shaped outer surface 92 configured to engage, slide, mate,wedge, or otherwise contact a corresponding opposing tapered or shapedinterior wall surface 94 of cavity 86. Upper clamp body 90 is movablewith respect to lower clamp body 88 to clamp down and affix cord 18 withrespect to end body 82. In one variation, upper clamp body 90 has a pairof downwardly extending arms 96 having openings 98 configured anddimensioned to receive protrusions or prongs 100 extending outward fromlower clamp body 88 so as to allow unidirectional clamping or locking ofend 46 with respect to cord 18. Arms 96 are configured and dimensionedto deflect or bend outward slightly to move over protrusions 100. Toaffix or clamp cord 18 with respect to end 46, upper clamp body 90 maybe assembled over lower clamp body 88 with cord 18 positionedtherebetween. As shown in FIG. 12, cord 18 may be additionally cinched,clamped, or locked when the assembled upper and lower clamp bodies 90,88 are positioned within cavity 86 and pulled or forced longitudinallyagainst the tapered inner wall 94 such that the outer surface 92engages, slides, mates, or wedges thereagainst to force the upper andlower clamp bodies 90, 88 to contract upon cord 18 such that a cordextending through the clamp bodies 88, 90 may not slide or move withrespect to end 46. One skilled in the art may appreciate that such atapered arrangement facilitates secure clamping during natural movementof flexible connection element 40 when installed. In one variation, ashoulder portion 102 of end body 82 may extend outward from flange 84and may extend into a portion of bumper 42.

Referring to FIGS. 12A-12D, another embodiment of a clamp assembly 104for clamping rigid stop, flange, or end portion 46 to cord 18 is shown.Clamp assembly 104 generally comprises an annular end body 82 having acentral cavity 86 and an end plate or flange 84 configured anddimensioned to house an insertable clamp body 105. Clamp assembly 104generally comprises a post or piercing means to affix cord 18 withrespect to end portion 46. In one variation, insertable clamp body 105has a central finger or post 106 extending downwardly from the undersidethereof. In one variation, the post 106 may be configured anddimensioned to extend through the cord 18 so as to puncture or piercethrough cord 18 and the distal tip 107 of post 106 may enter into adepression 108 provided on the interior of central cavity 86. Insertableclamp body 105 is movable with respect to clamp body 82 to puncture,pierce and/or clamp down and affix cord 18 with respect to end body 82.In one variation, insertable clamp body 105 has a pair of arms 109configured and dimensioned to engage clamp body 82 so as to allowunidirectional one step clamping, piercing, and/or locking of endportion 46 with respect to cord 18. As shown in FIGS. 12A-12B, in afirst position, insertable clamp body 105 may be spaced from orrelatively loosely affixed to end body 82 such that a cord extendingthrough cavity 86 may slide or move with respect to end body 82. Toaffix or clamp cord 18 with respect to end portion 46, insertable clampbody 105 may be forced downward further onto end body 82 and positionedin a second or locked position as shown in FIGS. 12C-12D. As shown inFIGS. 12C-12D, in the second position, insertable clamp body 105 may berelatively rigidly affixed to end body 82 such that a cord extendingthrough cavity 86 may not slide or move with respect to end portion 46.

In general, the flexible connection elements described herein can beextended to stabilize two or more joints or spinal motion segmentsbetween three or more adjacent vertebrae, and affixed to respectivevertebrae by three or more fasteners. Thus, in one exemplary embodiment,shown in FIG. 13 a flexible connection element 110, similar toconnection element 40 of FIG. 5 includes a plurality of spacers forproviding flexible stabilization to a plurality of joints or spinalmotion segments. In the embodiment of FIG. 13, a constrained spool 112may be provided at a first end 114, and unconstrained spools 116, 118and spacers 120, 122 may be interposed between a bumper 124 and clampassembly 126 disposed on a second end 128. Additionally, the spacers120, 122 may be alternated with various spool members (i.e. constrainedor unconstrained) in any order or combination as needed by the surgeon.Further, an additional bumper may be positioned outside the first endsuch that a bumper would be provided at opposite ends of the construct.In this way, a hybrid multi-level or multi-spine segment connection unitmay be designed, wherein each segment of the connection unit can providea desired level of flexibility suited for each respective pair ofinferior and superior vertebrae to be stabilized. For example, a firstsection of the connection unit that stabilizes a first pair of vertebraemay be very rigid, while a second section of the connection unit thatstabilizes a second pair of vertebrae may be more flexible when comparedto the first section. Numerous desired combinations of sections may beachieved to create a hybrid multi-level or multi-segment connectionunit, in accordance with the present invention.

Referring to FIG. 14, in one aspect of the invention one or more angledor lordosed spools 130 may be provided to form a construct or flexibleconnection element 131 to conform to and/or restore the natural lordosisof the spine. Spools 130 may be similar to spools 45, 47 described aboveexcept the end plates or flanges 132 may have an angle 134 or be taperedwith respect to the normal of longitudinal spool axis 136. In oneembodiment, the angle 134 of the end plate 132 is between about 3.5degrees and about 5 degrees. In one variation, the end plate 132 may beangled about 4 degrees.

Referring to FIGS. 15-16, single and multi-level versions of anotherembodiment of a flexible connection element 140 are shown. Flexibleconnection element 140 is similar to connection element 131 of FIG. 14except the end plates or flanges 132 of spools 130 are configured anddimensioned to extend over at least a portion of the adjacentintermediate portion or spacer 16. In this regard, end plates 132 ofspools 130 may have a cylindrical internal portion 142 configured anddimensioned to house an end of the adjacent spacer 16. One skilled inthe art may appreciate that such a configuration may resist sheartranslational forces when implanted adjacent a motion segment of thespine. Such an end plate feature may be provided on spools or endportions with or without lordosis or in any other embodiments of endportions described herein.

Referring to FIG. 17, another embodiment of flexible connection element150 is shown. Connection element 150 may be employed in a hybridprocedure employing fusion and dynamic stabilization. In this regard, anelongated end portion 152 may be provided and engaged between vertebraeto be fused and one or more adjacent vertebral levels can be dynamicallystabilized with the intermediate portion 16 engaged between end portions152, 154. End portion 152 may have a rod portion 156 integrated into aspool portion 158 and may include a clamping means 160, such as a setscrew, to affix cord 18 to end portion 152. In addition, a bumper 162may be provided adjacent a second end 164 to facilitate elongation ofthe dynamically stabilized level. Connection elements are alsocontemplated that would provide for multiple spine levels stabilized byfusion and multiple levels dynamically stabilized.

Referring to FIG. 18, another embodiment of a flexible connectionelement 170 is shown. Flexible connection element 170 may have one ormore cords 172 extending longitudinally between rigid end portions 174,176 and the one or more cords 172 may be tied or crimped into holes 178provided on end portions 174, 176. A central protrusion, prong, or nub180 may extend outward from the face of end plate or flange 182 and intoflexible intermediate portion 184 to enhance the physicalinterconnection of the intermediate portion 184 to end members 174, 176.

Referring to FIG. 19, an alternate embodiment of a flexible connectionelement 190 is shown wherein one or more cords 192 extend throughintermediate portion 194 and may be rigidly attached to a first endportion 196 and a threaded member 198. Threaded member 198 may bescrewed or threadedly attached to a second end portion 200. In thisregard, threaded member 198 may be rotatably advanced to change theamount of tension in the cords and thus alter the stiffness of theconstruct of flexible connection element 190.

Referring to FIGS. 20-22, another embodiment of an end member or portion210 and intermediate portion 212 of a flexible connection element isshown. In this embodiment, end member 210 has a generally spherical seator interface surface 214 that is configured to engage or contactintermediate portion 212. In another aspect of the invention, aprotrusion 216 may extend from interface surface 214 and extend intointermediate portion 212 to enhance the physical interconnection of theintermediate portion 212 to end member 210. In a further aspect, theanterior portion or bottom 218 of end member 210 and intermediateportion 212 may be flat to facilitate a low profile once installed. Itis also contemplated that such a flat bottom feature may be incorporatedin the many alternate embodiments described throughout thespecification. In a further aspect, a coupling member or cord 18 mayextend eccentrically through intermediate portion 212. For example, inthe depicted embodiment, cord 18 may extend through intermediate portionadjacent the upper or posterior portion of spacer. In this regard, theflexible connection element constructed in such a fashion may be lessrigid on one side as compared to the other.

Referring to FIG. 23, an alternate embodiment of a flexible connectionelement 220 is shown wherein the coupling member or cord 18 extendsalong the top or posterior side of intermediate portion 16 and may besecured or affixed to end members 224, 226 by a top mounted set screwlock 228. As a result, like previously described embodiments theflexible connection element constructed in such a fashion may be lessrigid on one side as compared to the other.

Various embodiments of flexible connection elements contemplatealternative end members or portions configured to engage alternativebone fasteners or anchors. In particular, the embodiments of FIGS.24-54, discussed below, are generally configured to engage a post typeanchor or bone screw. In general, these embodiments have at least oneend portion comprising a hole or opening configured to receive theposted end of the bone anchor therethrough. However, one skilled in theart may appreciate that these embodiments may be modified to engage atop loading, yoke, or tulip type receiving member of an anchor.

Referring to FIGS. 24-25, another embodiment of a flexible connectionelement 230 is shown that is configured and dimensioned to engage aposted screw or bone fastener. According to one variation, the flexibleconnection element 230 may comprise an intermediate body portion 232interposed between opposite end portions 236, 238. Intermediate bodyportion 232 may be made from a similar resiliently deformable materialas intermediate portions described above and may be molded over andbetween end portions 236, 238. In one aspect of the embodiment, endportions 236, 238 may define a generally cylindrical opening 240 toaccommodate a shaft therethrough, such as a shaft or post end of aposted screw fastener. In this regard, flexible connection element 230is generally configured and dimensioned to be coupled to and tointerconnect between two bone fasteners, one coupled to each end portion236, 238. In one variation, end portions 236, 238 may each comprisesrigid sleeves or annular rings which may be encapsulated or molded intothe material of the intermediate body portion. For example, ifintermediate body portion is made from a polymer material, the polymermay be molded over annular rings 236, 238. In another aspect,intermediate body portion 232 may have a rounded profile and may extendin the posterior direction a sufficient distance to cover or extendbeyond a nut or other clamping member assembled upon the posted screwand engaging end portions 236, 238. In general, when a nut or clampingmember is assembled upon the end or post portion of anchor 234, it sitsdown in a low profile position. In one variation, flexible connectionelement 230 may elongate and compress due to the elastic or resilientproperties of the material of the intermediate portion without anintegrated coupling member or cord. In alternate embodiments, one ormore coupling members or cords may be provided extending about endportions 236, 238 and may or may not be molded into intermediate portion232 to facilitate the flexible movement of connection element 230.

Referring to FIG. 26, another embodiment of a flexible connectionelement 240 is shown wherein the intermediate portion or spacer (notshown) may be molded between end portions 244, 246. In this embodiment,end portions 244, 246 generally have an opening 248 to house a mountingblock 250 and one or more cords 252 may be fixed to the end portion 244by mounting block 250. Mounting block 250 may be pinned into the housing248 by a post or pin member 255. In one variation, one or more sideholes 254 may be provided in the housing 248 to allow the spacermaterial to flow out through the openings during injection molding tomechanically lock the housing 248 to the intermediate portion. In oneembodiment, the cord or cords 252 may be locked into block 250 bywinding. The cord or cords 252 may be aligned in a medial/lateral oranterior/posterior direction. In this embodiment, the flexibleconnection element 240 may elongate due to the flexible properties ofthe cord itself. In one variation, the end portions 244, 246 may have aflat section 256 surrounding an opening 258 in the end portion toaccommodate multi-level stacking or serial connection in the spine. Inthis regard, the flexible connection elements 240 may be flipped over orjuxtaposed to facilitate face to face contact of flat sections 256 andnesting of each flexible connection element 240. One skilled in the artmay appreciate, that such a feature facilitates a low profileconstruction in addition to allowing for implantation over multiplelevels.

FIG. 27 is a perspective view of another embodiment of a flexibleconnection element 270. In this embodiment, a generally flattened band272 may extend around end spools 274, 276 and about the periphery of theconnection element 270. A spacer body 278 may be made from a similarresiliently deformable material as intermediate portions described aboveand may be molded over and between end spools 274, 276 and band 272. Inone variation, band 272 may be made from a metal material such astitanium, spring steel, or other suitable material. According to oneaspect, in this embodiment, band 272 may have one or more bends 278 orcrimps along its length to allow for elastic deformation of the band 272and/or separation or retraction of end portions 274, 276 andfacilitating the return to the default position or configuration. Inanother variation, cover or spacer body 278 may facilitate elasticdeformation under compressive forces (i.e. when spools 274, 276 areforced closer together). In this regard, the cover body 278 mayresiliently deform to block the compressive movement and after thecompressive force dissipates the cover body 278 may restore itself toits original shape, thereby restoring the spacing between spools 274,276 and the screws attached thereto. Like the embodiment of FIG. 26,described above, flexible connection element 270 may comprise a singlesegment in a multilevel construct. In this regard, the end portions 274,276 may be juxtaposed to facilitate face to face contact of generallyflat sections 279.

Referring to FIG. 28, in a modification of the embodiment shown in FIG.26, flexible connection element 280 may have one or more cords 282extending longitudinally between end portions 284, 286 and the one ormore cords may be tied or crimped into holes 288 provided on end members284, 286. The flexible intermediate portion 288 may be molded aroundpins 290 to enhance the physical interconnection of the intermediateportion 288 to end members 284, 286. According to this embodiment,intermediate portion 288 may have a generally cylindrical shape with agenerally circular cross-section.

Referring to FIGS. 29-34, various alternative cord connection mechanismsare shown. In the embodiment of FIGS. 29-30, at least three cords 301,302, 304 are provided with at least two cord portions 302, 304 extendingalong the lower, bottom or anterior portion and at least one cordportion 300 along the upper, top, or posterior portion of intermediatesection 306. As with previous embodiments, intermediate section 306 maybe made from an elastically resilient deformable material such aspolycarbonate urethane or the like and the end members 308, 310 may bemade from a suitable rigid material such as titanium or the like. Cord301 provided along the upper portion of intermediate section 306 may beselectively lengthened or shortened prior to implantation to shape theflexible connection element 300 to accommodate lordosis. In this regard,if the upper cord portion 301 is shortened the flexible connectionelement 300 will bow or curve in the posterior direction. In anothervariation, the lower cord portions 302, 304 may be parts of a singleloop of cord extending around the periphery of end members 308, 310 ofthe flexible connection element 300. In addition, one may appreciatethat such a configuration may provide different levels of stiffness inthe anterior-posterior direction. This may be advantageous if it isdesired to provide a greater level of stiffness when the flexibleconnection element 300 is flexed during spinal extension (e.g., when apatient bends backward) and a lesser level of stiffness when theflexible connection element 300 is flexed during spinal flexion (e.g.,when a patient bends forward). Thus, flexible connection element 300 canprovide different levels of stiffness in different directions ofmovement and, hence, varying levels of stability can be provided todifferent directions of movement of a vertebra secured thereto.

Referring to FIGS. 31-32, in a modification of the embodiment shown inFIGS. 29-30, upper cord 301 may be coupled or fixed to end members 308,310 with a mechanical spring biased binding mechanism or member 320similar to a karabiner. Referring to FIGS. 33-34, in anothermodification of the embodiment shown in FIGS. 29-30, cords 302, 304 maybe moldably attached to end members 308, 310 and an upper cord 301 maybe fixedly attached with one or more set screws 324 and hence adjustedor tensioned to create lordosis as explained above. Bottom or lowercords 302, 304 may have enlarged lead ends 326 configured anddimensioned to fit or key into corresponding eye holes 328 in endmembers 308, 310.

Referring to FIG. 35, a saggital plane view shows a plurality offlexible connection elements 300 similar to the embodiment shown inFIGS. 33-34 situated in a serial juxtaposed position to form anexemplary multilevel construct. In this regard the adjacent flexibleconnection elements are flipped, or inverted to facilitate a face toface positioning or contact of flat sections 330 of end portions 308,310. One skilled in the art may appreciate that a post or shaft portion336 of a bone fastener or screw may extend through two adjacent flexibleconnection elements.

Referring to FIGS. 36-37, in a modification of the embodiment shown inFIGS. 33-34, end member 362 of flexible connection element 360 may havea flexible slit 364 that is compressible on a posted type screw or bonefastener. In this regard, the flexible slit 364 comprises a deflectableor deformable portion configured and dimensioned to deform, collapse, orcompress to engage with a spherical or ball shaped feature that may beprovided, for example, on a shaft of a post type screw. In operation,the end member 362 of this embodiment may be secured to a post typefastener without the need for more than one nut or clamping member whentwo end members are attached to a single post type screw. One skilled inthe art may appreciate that such a configuration may facilitate thestacking or juxtaposition of flexible connection elements 360 in amultilevel construct as shown in FIG. 35.

Referring to FIG. 38, another embodiment of an end member 380 is shown.In this embodiment, a modified protrusion, rib, or key portion 382extends from internal face 384 of end member 380. Similar to previousdescribed embodiments, protrusion 382 is configured and dimensioned tomate, extend into, or otherwise engage a correspondingly shapedindentation in an intermediate portion and to mechanically interface orconnect therewith. In this variation, protrusion 382 has a generallyarcuate or curved convex surface 386 extending in the anterior-posteriordirection and has generally flat or planar side walls 388. In operation,curved surface 386 generally facilitates rotational or pivotal relativemovement in the anterior posterior direction between end member 380 andan intermediate portion. Side walls 388 meanwhile generally prohibitrelative movement between the end member and the intermediate portion ina medial-lateral direction.

Referring to FIGS. 39-41, additional embodiments of flexible connectionelements 390 are shown. As best seen in FIG. 40 wherein one variation ofa bottom portion of a clamp member is shown, clamp member 392 definingone or more generally spherical socket portions 394 may be provided toclamp or hold a ball shaped end member 396 of flexible connectionelement 390. The ball shaped end member 396 allows selectably fixableangulation of flexible connection element 390 with respect to a posttype screw as shown in FIG. 39. Once a desired angle is selected, theclamp member 392 may be compressed by, for example, a nut 398 to clampdown and affix end member 396 within socket portion 394. According toone embodiment, once the clamp member 392 is so affixed, no furthermovement or angulation between clamp member 392 and end member 396 iscontemplated to occur without loosening or unclamping clamp member 392.Referring to FIG. 41, in a modification of the embodiment of FIG. 39,clamping member 392 of flexible connection element 400 may have socketportions offset from the longitudinal axis 402.

FIG. 42 depicts another embodiment of an end member 410. In thisembodiment, modified grooves, passageways, slots or indentations 412,414 are provided to accommodate the extension of a coupling member orcord therethrough or thereabout. In this regard, a posterior groove 412extends about the outer periphery of an upper portion 416 and isgenerally configured and dimensioned to accommodate, hold, or capture aposterior cord loop. An anterior groove 414 extends about the outerperiphery of a lower portion 418 with a generally angled downwardsection 420 adjacent the lateral edges. Like posterior groove 412,anterior groove 414 is generally configured and dimensioned toaccommodate, hold, or capture an anterior cord loop.

Referring to FIGS. 43-45, another embodiment of flexible connectionelement 430 is shown wherein the coupling member comprises a looped cord432 having an internal twist or crossed over portion. Intermediateportion 434 has an internal opening 436 configured and dimensioned toprovide clearance or space to allow cord 432 to twist and tension. Oneskilled in the art may appreciate that the more cord 432 twists, theshorter the distance between end members 438, 440 may get, and hence theoverall tension or stiffness of the construct may correspondinglyincrease. In this regard, the overall tension or stiffness of theconstruct may be controlled.

Referring to FIG. 46, the flexible connection element 460 may have anarcuate shaped interface 462 between end portions 464, 466 andintermediate portion or spacer 468. In this embodiment, four couplingmembers or cords may extend between end members 464, 466. Clampingplates 470 may be provided on each end member adjacent the top andbottom of flange portion 472 to secure, clamp, or affix the cords to theend member.

Referring to FIG. 47, in a modification of the embodiment shown in FIG.46, end members 464, 466 may have a laterally positioned opening 474 forside mounting to a post type screw. In this embodiment, an upper andlower coupling member or cord 476 may extend through intermediateportion 478 and clamping plates 480 may be provided on each end memberadjacent the top and bottom of flange portion to secure, clamp or affixcords 476 to the end member.

Referring to FIG. 48, in a modification of the embodiment shown in FIG.47, intermediate portion 490 and end members 492, 494 may have a trough,indentation, or groove 496 extending along the top and bottom of theconstruct and may be configured and dimensioned to accommodate acoupling member or cord therein.

Referring to FIG. 49, an alternate side mountable end portion 500 isshown. In this variation, a hole 502 may be provided to accommodate aset screw to secure cord 504 to end member 500. A similar end portion500 may be provided on an adjacent bone anchor and cord 504 may couplethem together with intermediate portion 506 disposed therebetween.

Referring to FIGS. 50-51, an alternate flexible connection element 510may have an intermediate portion 512 with a generally ovoid or footballshape and may have an indentation, groove, or trough 514 extendingaround the periphery and generally aligned and coextensive with anindentation, groove or trough 516, 518 extending about the periphery ofend members 520, 522. When assembled, troughs 514, 516 and 518 extendabout the periphery of flexible connection element 510 and areconfigured and dimensioned to accommodate a coupling member or cord 524in the shape of a continuous loop. In operation, when end members 520,522 are compressed together, intermediate portion 512 may be resilientlycompressed and/or deformed and when end members are separated, couplingmember or cord 524 may be resiliently elastically elongated. As shown inFIG. 51, in one variation the embodiment of FIG. 50 may be used inseries with another flexible connection element 510 for spinestabilization over multi levels or motion segments.

Referring to FIG. 52, in a modification of the embodiment shown in FIG.50, coupling member or cord 524 may extend internally throughintermediate portion 512 and externally around the periphery of endportions 520, 522.

Referring to FIGS. 53-54, in an alternate embodiment of a flexibleconnection element 540, end members 542, 544 may have an angled endplate or flange 546 to interface with intermediate portion 548. Oneskilled in the art may appreciate that such an angled flange featuresaves space and facilitates installation of flexible connection element540 in motion segments where space constraints dictate. For example,flexible connection element 540 may be utilized at the L5-S1 level. Asshown in FIG. 54, a multilevel construct may be provided with an endportion having angled flange portions 546, 547 on both sides of boneanchor 550 such that flanges 546, 547 may both engage intermediateportions or spacers 548.

Bone Fasteners

The bone fasteners included in the disclosed system include any type offastener that may be attached to the flexible connection element of theinvention, while remaining securely fastened onto the intended bone.Thus, the bone fasteners may include mono-axial screws, polyaxialscrews, post-type screws, helical blades, expandable screws, such asMollie bolt type fasteners, which are inserted or screwed into the boneand expand by way of some type of expansion mechanism, conventionalscrews, staples, sublaminar hooks, and the like. In one embodiment, thebone fasteners are coated with any number of suitable osteoinductive orosteoconductive materials to enhance fixation in the bone. In anotherembodiment, the bone fasteners are fenestrated to enhance bony ingrowthor to further anchor the fastener to the bone.

The bone fasteners may be made from a host of materials. For example,the fasteners may be formed from natural/biological materials, such asallograft, xenograft, and cortical bone. The fasteners may also beformed from synthetic bioresorbable materials, such as polyanhydride,polylactide, polyglycolide, polyorthoester, polyphosphazene, calciumphosphate, hydroxyapatite, bioactive glass, tyrosine-derivedpolycarbonate, and mixtures thereof. In another embodiment, thefasteners are formed from non-bioresorbable materials including, but notlimited to, stainless steel, titanium, titanium alloys, cobalt chromealloys, shape-memory alloys, and carbon-reinforced polymer composites.

In addition, the fasteners may include growth factors for bone ingrowthand bony attachment, or for soft tissue ingrowth. Non-limiting examplesof growth factors include insulin-like growth factor 1, basic fibroblastgrowth factor, transforming growth factor β-1, platelet-derived growthfactor, bone-derived growth factors, arginine, bone morphogeneticprotein, LIM mineralization protein, and combinations thereof

As mentioned previously, the flexible connection element also may beused in other component of a spinal fixation system. For instance, itmay be used as part of a transconnector. In this embodiment, theflexible connection element may be disposed between two fastenersconnected to rods positioned along the length of the spine. Any fastenerthat may be suitable for a conventional transconnector may be used withthe present invention. Some examples of fasteners are described in U.S.Pat. No. 6,565,565 to Yuan, U.S. Pat. No. 6,562,040 to Wagner, U.S. Pat.No. 6,551,318 to Stahurski, and U.S. Pat. No. 6,540,749 to Schafer, allof which are incorporated herein in their entireties.

Assembly of the System

The flexible connection element may be connected to fasteners in anumber of ways, i.e., so that the connection is constrained,unconstrained, articulated, or combinations thereof. For example, theend portions may be attached to bone anchors and inserted or installedadjacent a motion segment of the spine. The flexible connection elementmay be inserted into or onto anchor heads, which can be side-loading ortop-loading in this aspect of the invention. Following the placement ofthe flexible connection element upon the anchor heads, clamping screwsmay be inserted into or upon the anchor heads and firmly screwed downsecuring all the connected elements in place. This design wouldgenerally allow flexibility between the two bone fasteners.

The stiffness of the disclosed systems may also be adjusted during theoperation and post-operation using a set screw. This would allowsurgeons and doctors to make adjustments depending on a specificscenario.

The system, once assembled, may serve a variety of functions in themotion segment unit. For example, the system may reduce the load on thedegenerative disc and/or facet joints in the motion segment unit. Inaddition, the height of the adjacent vertebrae may be restored toeliminate crushing or slipping of the disc therebetween. Moreover,lordosis may be created/preserved using the disclosed systems in atleast one motion segment unit of the spine. Furthermore, the stiffnessof the motion segment unit may be restored with the implementation ofthe system of the invention.

In some embodiments, flexible connection elements may be disposed incombination with rods used to make a portion of the system rigid. Forexample, a motion segment neighboring a treated area that has beenessentially immobilized with a rigid stabilization system may besupported with a flexible connection element.

While it is apparent that the invention disclosed herein is wellcalculated to fulfill the objects stated above, it will be appreciatedthat numerous modifications and embodiments may be devised by thoseskilled in the art.

What is claimed is:
 1. A spine stabilization system, the systemcomprising: an elongate connection element extending from a first endportion to a second end portion along a longitudinal axis, the first andsecond end portions interconnected by a flexible coupling member, theelongate connection element comprising a first attachment portion, asecond attachment portion, a first resilient member positioned betweenthe first end portion and the first attachment portion, and a secondresilient member positioned between the first attachment portion and thesecond attachment portion, wherein the elongate connection elementpermits motion of the first attachment portion relative to the secondattachment portion, wherein the first and second attachment portionscompress the second resilient member when the first and secondattachment portions move towards each other, and wherein the first endand first attachment portions compress the first resilient member whenthe first and second attachment portions extend away from each other; afirst fixation member operably connected to the first attachmentportion, wherein the first fixation member comprises a first head havinga first channel, wherein the first attachment portion is received in thefirst channel; and a second fixation member operably connected to thesecond attachment portion, wherein the first end portion is a free end,wherein the second fixation member comprises a second head having asecond channel, wherein the second attachment portion is received in thesecond channel.
 2. The system of claim 1, wherein the coupling member isa cord.
 3. The system of claim 2, wherein the first attachment portion,second attachment portion, first resilient member and second resilientmember are coaxial with the cord.
 4. The system of claim 1, wherein thecoupling member is made from a polyethylene material.
 5. The system ofclaim 1, wherein the first end portion and second end portion arerigidly fixed to the coupling member.
 6. The system of claim 5, whereina portion of the first and second end portions pierce the couplingmember.
 7. The system of claim 5, wherein a portion of the first andsecond end portions clamp the coupling member.
 8. The system of claim 5,wherein the first attachment portion is slidable with respect to thecoupling member and the second attachment portion is integral with thesecond end portion.
 9. The system of claim 8, wherein the first andsecond attachment portions comprise spools.
 10. The system of claim 8,wherein the second end portion comprises an elongate rod.
 11. The systemof claim 1, wherein the elongate connection element is curved in aneutral position to accommodate the lordosis in the spine.
 12. Thesystem of claim 1, wherein the resilient members are made of a urethanematerial.
 13. The system of claim 12, wherein the resilient members havea durometer between about shore 80 A to about shore 100 A.
 14. Thesystem of claim 1, wherein the first fixation member comprises a pediclescrew.
 15. The system of claim 14, wherein the pedicle screw is amulti-axial pedicle screw.
 16. The system of claim 1, wherein the firstand second resilient members are made from materials having a differenthardness.
 17. The system of claim 1, wherein the first and secondattachment portions may extend away from each other up to 4 mm.
 18. Aflexible elongate connection element, comprising: an elongate bodyextending from a first end portion to a second end portion along alongitudinal axis, the first and second end portions interconnected by aflexible coupling member, the elongate body comprising a firstattachment portion, a second attachment portion, a first resilientmember positioned between the first end portion and the first attachmentportion, and a second resilient member positioned between the firstattachment portion and the second attachment portion, wherein theelongate connection element permits motion of the first attachmentportion relative to the second attachment portion, wherein the first andsecond attachment portions compress the second resilient member when thefirst and second attachment portions move towards each other, andwherein the first end and first attachment portions compress the firstresilient member when the first and second attachment portions move awayfrom each other; wherein the first attachment portion is configured tobe attached to a first bone fastener, wherein the first bone fastenercomprises a first threaded portion attached to a first head forming afirst channel, wherein the first attachment portion is received in thefirst channel of the first bone fastener; and wherein the secondattachment portion is configured to be attached to a second bonefastener, wherein the second bone fastener comprises a second threadedportion attached to a second head forming a second channel, wherein thesecond attachment portion is received in the second channel of thesecond bone fastener.
 19. The connection element of claim 18, whereinthe body is a rod that is top loadable into pedicle screws.
 20. Theconnection element of claim 18, wherein the first attachment portioncomprises an upper clamp element and a lower clamp element, wherein theupper clamp element extends along sides of the lower clamp element.